1. Field of the Invention
This invention relates to a heat exchanger for medical treatment. More particularly, it relates to a heat exchanger for medical treatment to be used in the extracorporeal circulation of blood for the purpose of maintaining the temperature of the blood at a desired level during the course of the circulation.
2. Description of the Prior Art
Extracorporeal blood circulation is generally employed as an auxiliary measure for surgery of the heart, particularly for cardiotomy. In the extracorporeal blood circulation as an auxiliary measure for cardiotomy, the blood drawn out of the patient's body is forwarded to an oxygenator, there to be oxygenated, and then returned in an oxygen-saturated state back to the patient's body. In the surgical operation performed on a complicated infantile cardiac deformation or on an adult aortic aneurysm, for example, the extremely low body temperature extracorporeal circulation method or the medial body temperature extracorporeal circulation method is employed. This blood circulation is effected by cooling the blood drawn out of the patient's body. In the extracorporeal body circulation of the nature under discussion, the blood drawn out of the patient's body must be kept at a prescribed temperature or cooled or heated. For this purpose, it has been customary to use a heat exchanger in the circuit for the extracorporeal blood circulation.
The heat exchangers developed to date for use in extracorporeal blood circulation are widely varied in type. For example, a shell-and-tube exchanger 1 which, as illustrated in FIGS. 1 and 2, comprises a first fluid passing space 2 and a multiplicity of heat-exchanging tubes 4 disposed inside the first fluid passing space 2 in the longitudinal direction of the first fluid passing space 2 and provided with an inner space 3 destined to form a second fluid passing space watertightly separated from the first fluid passing space 2 is a highly hopeful heat exchanger for medical treatment which effects very efficient exchange of heat and enjoys exceptional compactness of design. When the first fluid passing space 2 is formed in a cylindrical shape, a first fluid inlet tube 5 for introducing a first fluid into the first fluid passing space 2 and a first fluid outlet tube 6 for discharging the first fluid from the first fluid passing space 2 are adapted, as illustrated in FIGS. 1 and 2, so as to be extended inwardly from outside substantially along the straight line passing the central part of a cross section perpendicular to the axis of the first fluid passing space 2 and consequently allowed to communicate with the first fluid passing space 2.
When the shell-and-tube exchanger 1 constructed as described above is used in effecting exchange of heat between the blood and the heat-exchanging medium by passing the heat-exchanging medium through the first fluid passing space 2 and the blood through the second fluid passing space, i.e., the inner spaces 3 of the heat-exchanging tubes 4, the exchange of heat can be accomplished substantially uniformly on all of the blood because the blood is distributed comparatively uniformly and allowed to keep a relatively constant contact with respect to the heat-exchanging medium. When the pressure loss during the introduction of the blood is large and the extracorporeal blood circulation lasts for a long time, a fair possibility ensues that the blood will be coagulated inside the inner spaces 3 of the heat-exchanging tubes 4 and will consequently clog or constrict the heat-exchanging tubes 3. Conversely, when the exchange of heat is carried out by passing the blood through the first fluid passing space 2 and the heat-exchanging medium through the second fluid passing space or the inner spaces 3 of the heat-exchanging tubes 4, the aforementioned possibility of the blood conduits being clogged or constricted is substantially precluded and the pressure loss due to the introduction of the blood is repressed to a comparatively large extent. Since the first fluid inlet tube 3 and the first fluid outlet tube 6 are adapted, as described above, so as to be extended inwardly from outside substantially along the straight line passing the central part of a cross section perpendicular to the axis of the first fluid passing space 2 and consequently allowed to communicate with the first fluid passing space 2, the blood mainly advances toward the central part of the first fluid passing space 2 and consequently the flow of the blood inside the first fluid passing space 2 is not uniform but is varied locally. In the region of relatively high blood flow, exchange of heat is effected to an unduly small extent because the blood does not sufficiently contact the heat-exchanging tubes 4 now passing the heat-exchanging medium inside the inner spaces 3 thereof. By contrast, in the region of relatively low blood flow, the exchange of heat is effected to an unduly large extent because the blood contacts the heat-exchanging tubes 4 more than is normally required. Where the heat-exchanging tubes 4 are distributed throughout the whole blood passing space 2 as illustrated in FIGS. 1 and 2, the unfavorable situation mentioned above grows in conspicuity because the blood introduced through the blood inlet tube 5, on entering the blood passing space 2, comes into direct contact with the heat-exchanging tubes 4 and, consequently, the blood flow is not uniformly distributed throughout the entire blood passing space 2. The shell-and-tube exchanger which is incapable of effecting exchange of heat uniformly on all of the blood being passed therethrough thus, there is the possibility of impairing the uniformity of blood temperature distribution, exchanging heat excessively or insufficiently, exchanging heat and bringing about adverse effects upon the blood components.
Further, the conventional heat exchanger is so constructed that a heat-exchanging medium inlet port for introducing the heat-exchanging medium into the heat exchanger and a heat-exchanging medium outlet port for discharging the heat-exchanging medium from within the heat exchanger are integrally formed with a housing of the heat exchanger and are fixed on the housing. A connection tube which leads out of a heat-exchanging medium temperature controller communicating with the heat-exchanging medium inlet port and the heat-exchanging medium outlet port is generally large in diameter and hard to the touch. The connection between the coupler disposed on the heat-exchanging medium inlet port or the heat-exchanging medium outlet port and the coupler disposed at the leading end of the connection tube of the heat-exchanging medium temperature controller is obtained only with difficulty. Moreover, the possibility ensues that this connection will be dissolved in consequence of a deviation suffered to occur in the positional relationship between the heat exchanger and the heat-exchanging medium temperature controller during the course of operation.
An object of this invention, therefore, is to provide an improved heat exchanger for medical treatment.
Another object of this invention is to provide a heat exchanger for medical treatment which, in extracroporeal blood circulation, enables the blood drawn out of a patient's body to be kept at a desired temperature.
Yet another object of this invention is to provide a heat exchanger for medical treatment which effects uniform exchange of heat between the blood and the heat-exchanging medium and inflicts damage sparingly on the blood under treatment.
Still another object of this invention is to provide a heat exchanger for medical treatment which enjoys exceptional compactness of design and suffers from only a small pressure loss during the introduction of blood.
A further object of this invention is to provide a heat exchanger for medical treatment which is capable of being integrated with an oxygenator.
A still further object of this invention is to provide a heat exchanger for medical treatment which excels in operability and ensures great safety.